Shrimp

The following description refers mainly to the external anatomy of the common European shrimp, Crangon crangon, as a typical example of a decapod shrimp. The body of the shrimp is divided into two main parts: the head and thorax which are fused together to form the cephalothorax, and a long narrow abdomen. The shell which protects the cephalothorax is harder and thicker than the shell elsewhere on the shrimp and is called the carapace. The carapace typically surrounds the gills, through which water is pumped by the action of the mouthparts. The rostrum, eyes, whiskers and legs also issue from the carapace. The rostrum, from the Latin rōstrum meaning beak, looks like a beak or pointed nose at the front of the shrimp's head. It is a rigid forward extension of the carapace and can be used for attack or defense. It may also stabilize the shrimp when it swims backward.

Shrimp are widespread, and can be found near the seafloor of most coasts and estuaries, as well as in rivers and lakes. There are numerous species, and usually there is a species adapted to any particular habitat. Most shrimp species are marine, although about a quarter of the described species are found in fresh water. Marine species are found at depths of up to 5,000 metres (16,000 ft), and from the tropics to the polar regions. Although shrimp are almost entirely fully aquatic, the two species of Merguia are semi-terrestrial and spend a significant part of their life on land in mangrove.

Shrimp are marketed and commercialized with several issues in mind. Most shrimp are sold frozen and marketed based on their categorization of presentation, grading, colour, and uniformity. Shrimp have high levels of omega-3 fatty acids and low levels of mercury. Usually shrimp is sold whole, though sometimes only the meat of shrimp is marketed.

As with other seafood, shrimp is high in calcium, iodine and protein but low in food energy. A shrimp-based meal is also a significant source of cholesterol, from 122 mg to 251 mg per 100 g of shrimp, depending on the method of preparation. Shrimp consumption, however, is considered healthy for the circulatory system because the lack of significant levels of saturated fat in shrimp means that the high cholesterol content in shrimp improves the ratio of LDL to HDL cholesterol and lowers triglycerides.

There are many variations in the ways different types of shrimp look and behave. Even within the core group of caridean shrimp, the small delicate Pederson's shrimp (above) looks and behaves quite unlike the large commercial pink shrimp or the snapping pistol shrimp. The caridean family of pistol shrimp are characterized by big asymmetrical claws, the larger of which can produce a loud snapping sound. The family is diverse and worldwide in distribution, consisting of about 600 species. Colonies of snapping shrimp are a major source of noise in the ocean and can interfere with sonar and underwater communication. The small emperor shrimp has a symbiotic relationship with sea slugs and sea cucumbers, and may help keep them clear of ectoparasites.

Females of the freshwater shrimp Caridina ensifera are capable of storing sperm from multiple partners, and thus can produce progeny with different paternities. Reproductive success of sires was found to correlate inversely with their genetic relatedness to the mother. This finding suggests that sperm competition and/or pre- and post-copulatory female choice occurs. Female choice may increase the fitness of progeny by reducing inbreeding depression that ordinarily results from the expression of homozygous deleterious recessive mutations.

In 1991, archeologists suggested that ancient raised paved areas near the coast in Chiapas, Mexico, were platforms used for drying shrimp in the sun, and that adjacent clay hearths were used to dry the shrimp when there was no sun. The evidence was circumstantial, because the chitinous shells of shrimp are so thin they degrade rapidly, leaving no fossil remains. In 1985 Quitmyer and others found direct evidence dating back to 600 AD for shrimping off the southeastern coast of North America, by successfully identifying shrimp from the archaeological remains of their mandibles (jaws). Clay vessels with shrimp decorations have been found in the ruins of Pompeii. In the 3rd century AD, the Greek author Athenaeus wrote in his literary work, Deipnosophistae; "... of all fish the daintiest is a young shrimp in fig leaves."